Christine Forster, the PM’s sister, says same-sex marriage will become legal this year.

There is a delicious irony that under the stewardship of our Catholic, conservative Prime Minister, same-sex marriage looks likely to become a reality, finally, in Australia.

And it looks like Tony Abbott, the man who said he felt “threatened” by gay marriage, the man who said gay people challenged “the right order of things”, the man who said same-sex marriage was a “fashion of the moment” might just be attending his first same-sex marriage before the year is out.

Christine Forster on Lateline. ( ABC)

In the wake of the Irish same-sex marriage referendum last weekend the change looks likely to be through by the end of the year.

The sister of the Prime Minister, Liberal Councillor for the City of Sydney Christine Forster, said last night that gay marriage will be legal in Australia by the end of the year and she thinks her brother knows it is inevitable.

Ms Forster appearing on the ABC’s Lateline said it is “wonderful that the change to marriage laws will come under a conservative, deeply religious Prime Minister.”

“That will be for me one of the proudest moments of my life,” she said.

“To think that this reform comes under the prime ministership of Tony Abbott … I think it’s entirely appropriate that it would come under the Prime Ministership of Tony Abbott.

“At the end of the day I’m sure he will understand that this is good and fair for everybody and it will be great for Australia.”

The PM with his family when he was sworn in in 2013. ( Image: Getty)

Ms Forster said that the weekend vote in Ireland changed the landscape in Australia.

“The Irish vote, the very comprehensive, decisive, wonderful Irish vote over the weekend, it’s the watershed. It has proved to everybody that this very important reform that has been a long time coming, far too long coming from my opinion, is inevitable.”

She said she did not think her brother would actively would campaign against gay marriage in his party room.

“It’s not up to Tony to allow or disallow anything. There will be a debate and there will be a decision made by the party room,”

Ms Forster said she too believed that what was needed was a cross-party bill.

“[It is] the only way to get support for this across the Parliament and the Prime Minister was very clear about that in Question Time when Mr Shorten asked him yesterday. He said this has to be owned by the whole Parliament. It can’t just – it can’t be politicised. It can’t have one party’s name on it. We’ve got to do this together. It’s too important a change. It’s a nation-building change, so we have to do it together.”

Liberal backbencher Warren Entsch has confirmed that he is working with Labor MP Graham Perrett on a bipartisan same-sex marriage bill that will be brought on after the budget has passed the Parliament.

Mr Entsch, who earlier this week criticised Opposition Leader Bill Shorten for bringing on a Labor bill on the issue, said he was willing to work with several MPS on the issue including Greens senator Sarah Hanson-Young on a compromise bill.

Fairfax Media reports that Mr Perrett confirmed he was one of the Labor MPs prepared to work with Mr Entsch on the issue but only if the bill brought forward by Mr Shorten and deputy Labor leader Tanya Plibersek failed.

“The boss has something before the House now. Let’s see how that goes, if the [Liberal senator] Simon Birmingham and Warren can win the party room over.”

The PM has said it has to be a cross-party issue.

The Prime Minister on Wednesday indicted in parliament that it was up to his MPs and senators to decide whether to have a free vote – a move they are almost certain to support.

Christine Forster says it has been a long time coming “It’s been slower than I would’ve liked. It’s been slower than many of my colleagues would’ve liked. But I’ve always had full confidence that it was coming and that we would get there, and in the last few months, I’ve been increasingly confident that we would get there before the end of 2015.”

She said once the laws were changed she would marry her partner, Virginia and that her brother would be attending the wedding.

And on her mind, the one thing on every soon-to-be-married couple’s mind – the cost.

“The prospect for paying for half of what is going to be a very expensive wedding is a little daunting” said Ms Forster “but we will certainly – look, I haven’t checked in with her lately. Last time we discussed it, she was still game on. “